全新世以来洞庭湖的演变

EVOLUTION OF DONGTING LAKE SINCE HOLOCENE

本文根据全新世沉积物的岩性、岩相特征和文化遗址的时空分布,结合孢粉资料与历史文献记载,揭示了全新世以来洞庭湖演变的六个阶段:(1)晚更新世末至全新世初为河湖切割平原;(2)中全新世早、中期(8000—5000a B.P.)是湖泊扩展时期;(3)中全新世晚期(5000—3000 a B.P.)四水复合三角洲发育,湖沼洼地零星分布;(4)商周至秦汉(3000—1700 a B.P.)四水分流间洼地湖泊和沼泽广布,汛期河湖水体相连;(5)魏晋至19世纪中叶,洞庭湖逐渐发展至鼎盛阶段;(6)19世纪中叶至今,三角洲迅速推进,湖泊逐渐萎缩。研究认为这种发育演化过程与区域性气候变化、人类活动直接相关。

Dongting Lake, situated in the south of the middle reaches of the Changjiang River, is the second largest freshwater lake in China. According to the properties of sediments in Holocene and ancient cultural relics in various periods, as well as pollen data and historical records, the evolution of Dongting Lake can be divided into six stages.From later Pleistocene to early Holocene, Dongting Lake area was an alluvial plain with several small lakes and incised rivers since the level of the Changjiang River was 20-40 m lower than that of the present. During 8000 - 5000 a B. P. , with the rise of the water level in the Changjiang River resulted from high sea level, as well as warm palaeoclimate and plentiful rainfall, the water of four inlet rivers was jammed into this area to turn Dongting Lake into a large lake, an area starting from the Yuanjiang River mouth to Yueyang with a width of 17-33 km. During 5000-3000 a B. P. , the former large lake was divided by the four-river compound delta into several small lakes and swamps due to dry palaeoclimate. During 3000-1700 a B. P. , more than five large lakes and many swamps were formed in the lowland. From 1700 a B. P. to the 19th century, with the formation of Taiping Breach and Ouchi Breach relevant to the burst bank of the Changjiang River, and plentiful precipitation, Dongting Lake reached its largest area of 6000 km2. Beginning from the middle of the 19th century, as 0. 984 X 108 m3/a of silts carried in by the Changjiang River and four inlet rivers and a large-scaled reclaimed land from lake, Dongting Lake decreased rapidly to 2691 km2 in the 1980s.